Basic well drilling operations have remained unchanged over the years insofar that a number of connected drill pipes, forming a drill string, are rotated to turn a drill bit and abrade the earth formation. During drilling, it is necessary to measure various drilling parameters such as drilling formation, inclination, temperature, PH and the like. Because the drill string rotates, and in many cases thousands of feet below the earth's surface, gaining instantaneous downhole information has been a constant problem.
For example, the most efficient drilling operation occurs when the characteristics of the formation are known to the drilling operator. For different types of formations, such as rocks, soil or fluids and gases, it may be desirable to alter the surface operations to effectively deal with the type of formation in which the drill bit is presently encountering. Traditionally, the formation chips eroded by the drill bit are carried uphole in the annulus around the drill string by fluids pumped downwardly through the drill pipe. The inspection of these chips, however, is unreliable information of formation presently being drilled, as it may take a substantial period of time for the chips the ascend to the surface.
It is known in the art, i.e., U.S. Pat. No. 3,419,092, by Elenburg, that a dual passage drill pipe, in the nature of inner and outer concentric pipes, can be employed to pump aerated drilling fluid down one conduit to decrease the hydrostatic head at the drill bit and thereby accelerate the velocity by which the cuttings are moved upwardly to the surface in the other pipe conduit. In this manner, the cutting chips which represent the type of formation being drilled arrive at the surface more quickly, in which event the drilling operations can be modified accordingly. While fluid commutation to the various concentric conduits of the Elenburg-type drill pipe is relatively uncomplicated, the number of such conduits which can be employed is limited by practical considerations of the drill pipe construction.
In U.S. Pat. No. 2,951,680 by Camp et al., it is recognized that a non-concentric multi-conduit drill pipe may be employed to increase the number of conduits. However, to accommodate fluid commutation, the fluid passage transition from the conduits to the drill pipe end is convoluted into conventional concentric circular passages. As a result, commutation of different fluids into the respective conduits of the Camp et al. drill pipe was provided at the expense of complicating the manufacturability of the pipe, and thus making it costly.
Those skilled in the art have thus recognized the advantage of using multi-conduit drill pipes, but such pipes have not met with widespread success for a number of reasons. One drawback encountered in connecting such pipes together is the manner in which the conduits of one pipe are sealed to the conduits of another pipe. Conventional sealing arrangements include "0" rings or chevron seal rings (U.S. Pat. No. 2,951,680) or traditional packing (U.S. Pat. No. 3,077,358). Because of the type of seal used and the manner in which such seals have been used, the fluid pressure which the seals can withstand is generally under 7,500 p.s.i. differential.
It is apparent, therefore, that there is a need for a high-pressure multi-conduit drill pipe in which the number of conduits is not limited, nor is the structure or fabrication of the pipe unduly complicated or costly.
Moreover, there is an urgent need to monitor downhole drilling operations, instanteously transmit the results thereof uphole, and combine the transmission medium with the drill pipe in such a manner that the drill pipe fluid carrying capability is not severely compromised.
It has been heretofore proposed to employ the central bore of the drill pipe as a chamber in which an electrical conductor is situated. Exemplary of such practice is that disclosed in U.S. Pat. Nos. 2,795,397 and 3,904,840. According to this practice, however, the conductor insulation is subjected to the drill fluid, or expensive shielding must be used.
An attendant problem with the use of electrical conductors in the fluid-carrying bore is the isolation from the fluids of the electrical connections which connect lengths of conductors together. Elaborate and unusual techniques have been resorted to in order to circumvent this problem. To further compound the problem, the connection of conductors from one drill pipe to another is exacerbated in those types of pipes which require one section to be rotatably screwed into the other. In U.S. Pat. No. 2,748,358, this concern is dealt with by leaving ample cable length so that it may be twisted along with the pipe. In other instances, i.e., U.S. Pat. No. 3,879,097, the electrical cable is carried within the central bore along a majority of its length, except at the ends thereof where the cable is routed through the pipe sidewall to ring shaped contacts on the pipe ends. The number of conductors is obviously limited when resort is had to this technique.
Exemplary of prior provisions for connecting together a plurality of conductors at the pipe ends is that disclosed in U.S. Pat. No. 2,750,569. In this patent, the electrical cable is routed through the fluid carrying bore. This leaves the cable, as well as the connector, susceptible to the corrosive or erosive effects of the drill fluid.
Further concerns in the well drilling art which contribute to the overall expense incurred relate to the composition of the drilling "mud". The mud must be periodically adjusted with different materials and chemicals to effectively change its density, viscosity or other properties. This change can only be accomplished gradually as the mud circulates from the bit area upwardly through surface equipment. In some cases, such as an imminent blow out, the density of the mud must be altered very quickly to prevent such an occurrence. As a consequence, many blow outs cannot be averted with known techniques. A need has thus arisen for a drill string construction which allows the prompt altering of drill mud pressure to control blow outs and to otherwise enhance drilling.
Even after the drilling operation has been completed there is a need to monitor downhole parameters during the production phase for well management purposes. Conventional well casings have heretofore afforded a high degree of integrity to the well bore, but are ill-equipped to provide passageways for wires, gasses or liquids other than the fluid pumped upwards. As a stopgap measure, telemetry wires have been secured to the outer periphery of the casing by metal or plastic bands and extended downhole to telemetry equipment. It is also well known to provide parasitic pipes external to the casing for carrying air pressure to create artificial lift downhole.
As a result, there is a need for a multi-conduit well casing through which the production fluid can be pumped, as well as a plurality of additional conduits for housing telemetry wires and carrying solvents, antifreeze solutions and a host of other fluids.